Re: Action - Reaction Demo

["Ludwik Kowalski" <KowalskiL@Mail.Montclair.edu>]

Replying to Ken Fox  Donald E. Simanek wrote:

> .....   I fear that
> students will get from this demo a false idea of what an action/reaction
> pair of forces are. Newton's third: If body A exerts a force on body B,
> then B exerts and equal and opposite force on A. These forces, A and B,
> are an action/reaction pair.
>
> The situation of this demo is far too complicated for me to get a concept
> out of it.

To convince students that a force A can not exist alone I ask them to apply
hands to sticking nails, or other sharp objects. Are you convinced that
your hand is applying a force? Is there also another force, B, acting in the
opposite direction, that you feel at the same time? Then we generalize.
Squeezing a needle (or a clay ball) between two fingers is a little more
complicated because two action-reaction pairs are present.

Yes, forces are not visible but we do feel something when we push and
we know which way we are pushing. So we call this something a force.
And we also feel forces applied to our bodies, especially when sharp objects
are involved. In my course for non-science majors a force is simply
"a push or pull of any kind". Even when there is no touching, as for
magnets and gravity.

Ludwik Kowalski